Process and apparatus for solvent dewaxing of oils



Aug. 19, 1958 w. T. KNOX, JR., EIAL 2,848,372

PROCESS AND APPARATUS F OR SOLVENT DEWAXING 0F OILS Filed Sept. 1, 1954 i i, 20 I9 I l CHILLING ZONE ,22 I6 ,5 IO\ J I3! I I! DISTILLATION F'LTERWG ZONE ZONE U, DISTILLATION J ZONE &

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Fla-I I William 'T. Knox Jr. Inventors hen F. P rr Step 6 e y F 1 PROCESS AND APPARATUS FOR SOLVENT DEWAXING F OILS William T. Knox, Jr., Cranford, and Stephen F. Perry,

Westfield, N. J., assignors to Esso Research and Eng!- neering Company, a corporation of Delaware Application September 1, 1954, Serial No. 453,607

Claims. (Cl. 196-18) This invention relates to process and apparatus for the dewaxing of lubricating oils, and more particularly to process and apparatus useful in conjunction with the dewaxing of lubricating oils employing asolvent comprising a ketone.

It is well known that Wax can be recovered from waxy petroleum distillates by a process involving the addition of a dewaxing solvent to the distillate and subsequently chilling the resultant mixture of waxy distillate and solvent. Such chilling is normally carried out in tubular heat exchangers in which the mixture to be chilled passes through a plurality of pipes surrounded by a coolant. During the course of temperature reduction the wax is precipitated or rejected from the distillate and forms a slurry of oil, wax, and solvent. The precipitated wax tends to adhere to the inner surface of the tubes of the heat exchanger through which it is passed, and this necessitates the employment of mechanical scraping means in order to keep the inner surfaces of the tubes reasonably clear and to prevent fouling of the apparatus. While such mechanical scrapers may be employed in substantially rectilinear tubes, it is difiicult to adapt them for scraping the inner surface of curved tubes such as U-bends, which are normally present in conventional heat exchangers. In order to free these curved sections of the tubes from wax, it has been necessary to shut down the chiller and melt out the accumulated wax, as by passing hot oil through it. Such shutdowns necessitate multiplication of equipment, and are expensive and otherwise undesirable.

It is an object of the present invention to provide a process and apparatus for the dewaxing of oil using a ketone solvent that eliminates the necessity for periodic shutdowns by substantially preventing fouling due to wax deposition on the inner surface of the chiller tubes as well as on other surfaces with which the wax-oil mixture comes in contact during chilling, and more particularly a mechanical standpoint and also tends to deform the wax crystals, making subsequent separation of the wax more diflicult.

Additional objects will be in part apparent and in part particularly pointed out in the ensuing description.

The present invention comprises a solvent dewaxing process utilizing a dewaxing solvent comprising a ketone, wherein a mixture of wax and solvent is chilled, in which the chilling step is carried out in contact with a surface coated with phenol-formaldehyde polymer or condensation product. For purposes of the subsequent description, the term phenol-formaldehyde polymer includes condensation products also. It has been found that a coating of this material is eifective to prevent deposition of Wax under dewaxing conditions over a very substantial period of time, and further that such a coating is completely resistant to the solvent action of the dewaxing solvent, including the ketone constituent thereof,

States Patent The present invention will be more fully appreciated by reference to the drawings, in which:

Figure I is a diagrammatic representation of a typical solvent dewaxing process to which the improvement of the present invention is particularly adapted, and diagrammatically shows a chiller in which wax is rejected from waxy distillate; and

Figure II is a diagrammatic representation in vertical section of a portion of a chiller used in solvent dewaxing operation, illustrating the tubes which are lined internally with phenol-formaldehyde polymer and showing the scraping mechanism employed in the rectilinear portion of the tubes.

Turning now to Figure I, a waxy crude oil is introduced into the distillation zone 10 by means of feed line 11. Temperature and pressure conditions in zone 10 are adapted to remove overhead by means of line 12 the low boiling hydrocarbon fractions. A waxy distillate fraction is removed as a side stream by means of line 13, while a residual oil is removed by means of line 14-.

The waxy distillate flows to a chilling zone 15, after having been mixed with a suitable volume of dewaxing solvent including a ketone which is introduced through line 16. A typical operation is to introduce feed oil into the chilling stage 15 at a temperature of about F. It will be understood that while only a single chilling zone is shown in Figure I for the purpose of simplicity, it is the usual practice to carry out the chilling in a plurality of such zones arranged in series, usually about four in number, and cooling the oil-solvent mixture to a final temperature of about 0 F. at the exit end of the final stage. Wax deposition would normally occur in all of the chillers in the series.

After suitable chilling, the entire mixture comprising oily constituents, crystallized wax constituents, and solvent, passes through line 17 to the filter 18, wherein the solid wax particles are segregated from the oily constituents by any suitable filtering or separation means. The filtering zone may comprise filters, plate and frame presses, centrifuges, or suitable equivalent equipment for the separation of the precipitated Waxy constituents from the oily constituents. The oil and a portion of the solvent is removed from filter zone 18 via line 19, and the wax cake is washed with a wash solvent introduced into the filter zone through line 20. Slack wax and solvent are removed from filtering zone 18 by means of line 21 and passed to a distillation zone 22, wherein a separation is made between the wax and the solvent. It is to be understood that other means of seperating the solvent from the wax may be utilized if desirable. The wax may then be subjected to additional refining steps forming no part of the present invention.

Figure II illustrates diagrammatically a portion of the chiller 15 showing only two sets of pipes in which the chilling is carried out. It will be understood, of course, that a conventional chiller contains a plurality of pairs of such pipes, but only one set is shown for purposes of simplicity. The chiller is made up of a pair of cooling jackets 24a and 25a which surround rectilinear chilling pipes 24 and 25, respectively, which are connected by the U-bend 26. Each chilling pipe in the chiller assembly is jacketed in this way. The jacket is normally of about eight inches diameter, while the chilling pipe is about six inches in diameter. A cooling medium is employed in the cooling jackets 24a and 25a in heat exchange relation with the mixture oif oil, wax, and sol vent which flows through the connected pipes 24 and 25 in the direction indicated by the arrows and which is cooled through the walls of pipes 24 and 25. The pipes 24 and 25 each carry a shaft 27 mounted axially there of and suitably journaled in bearings 28, which'may be supported from the sides of the pipes or by other suitable a means. Mounted on the shaft 26 are the scraper blades 29 and 2911. These blades are each about two feet in length and are spring mounted or otherwise suitably attached to the shaft so that they will bear against the inner surface of the pipes 24 and 25. The shaft 27 is rotate'ed by suitable means not shown, and the scrapers remove wax deposited on the surface of the rectilinear pipes. According to the improvement of the present invention, the internal surface of the U-bend 26, which surface cannot practically be scraped by blades such as 29 and 29a, is coated with a thin layer of phenol-formaldehyde polymer. Preferably the coating is also applied to the entire inner surface of pipes 24 and as well as to all other metal surfaces in contact with the oil-wax-solvent slurry, namely, scraper blades 29 and 29a, the shaft 26, and the bearing supports 28. The polymer coating is preferably quite thin; a thickness of l to 2 mils (0.001-0002 inch) has been found elfective. This thickness of coating does not seriously impair the heat transfer through the pipe walls, which is, of course, necessary to effect proper cooling. The coating should be smooth and essentially free of discontinuities. It may be necessary to make two or more successive applications of the polymer to achieve this result, particularly on rough surfaces. The plastic film may be applied without the use of a primer coating simply by applying a solution of the resin to the surface, allowing it to dry in air for from five to eight minutes, and then heating to 325 F. for about twenty minutes. This causes the resin to polymerize or set up sufficiently to form a satisfactory plastic film.

Phenol-formaldehyde polymer of the type formed by curing an unmodified phenol-formaldehyde resin is found to be extremely effective in the prevention of wax deposition on metal surfaces. As will be pointed out in subsequent examples, it is able to withstand the solvent action of ketones within a wide temperature range, and is greatly superior for this purpose to other thermo-setting resins.

It is believed that the ability of phenol-formaldehyde polymer fihns to resist wax deposition may be due to both the extreme smoothness and the lack of porosity of such a surface and also to its chemical nature, which lacks affinity for the wax crystals and which may have a positive repelling effect thereon. Accordingly, it would be expected that even the slightest degree of attack on the film by either the solvent or the oil to be treated would destroy these necessary surface properties. Hence a film which is completely unaffected by the solvent-oil mixture, even at the most extreme conditions of temperature, is essential.

A coating of phenol-formaldehyde polymer serves two very useful purposes in solvent dewaxing. First, it may be used on surfaces which cannot conveniently be subjected to mechanical scraping so that it can prevent the gradual fouling with wax which necessitates periodic shutdowns and warrnups. Secondly, it may be used on surfaces which are normally scraped to prevent wax buildup, acting either to eliminate the necessity for scraping altogether, or at least to greatly reduce the amount of scraping required. Since it is known that scraping deforms wax crystals to such an extent that the filter rate of scraped wax is only about half of that obtainable without scraping, such a reduction is highly desirable from the standpoint of a continuous process. It is to be understood, however, that the present invention is not restricted to a dewaxing process in which scraping is eliminated entirely, since even a reduction of scraping obviously effects substantial economies.

In some cases an acid treating step will be employed on the feed stock entering the distillation zone 10, or the crude may contain naturally occurring acids, so that the waxy distillate entering the chiller 15 may be acid in nature. Such an acid stock tends to be corrosive to the chiller tubes, and it has been found that the plastic film of phenol-formaldehyde polymer is ineffective to prevent such corrosion over long periods of time. Another possible source of acidity is by degradation of the recirculated ketone solvent. It is preferred, therefore, that when carrying out a solvent dewaxing process utilizing the present invention, the charge should be substantiallly neutralized prior to introduction into the chiller. In such cases the addition of suitable neutralizing agents should be made to either the feed stock or solvent or both in order to maintain the pH of the oil-solvent mixture in the chiller at a value of at least 6. On the other hand, it is known that the phenol-formaldehyde resin composition is attacked by strong alkalies and hence an excess of any strong neutralizing agent must be avoided.

EXAMPLE I As an example of the efiicacy of phenol-formaldehyde polymer in inhibiting wax deposition on a metal surface under dewaxing conditions, a waxy distillate was mixed with 3.3 times its volume of dewaxing solvent containing 50% methyl-ethyl ketone, 29% benzol, and 21% toluol at a temperature of approximately F. and cooled by heat transfer through the walls of the container at the rate of 2.4 F. per minue to 0 F. The mixture was stirred with a three-bladed propeller turning at the rate of 240 R. P. M. throughout chilling. When this process was carried out in contact with a container wall of uncoated iron, it was found that a continuous, adherent coating of wax of 0.5 mm. thickness had been formed and that this deposit weighed 0.25 gram over a surface area of three square inches. The same chilling operation was carried out contacting the waxy mixture with an otherwise identical container wall which had been coated with phenol-formaldehyde polymer by brushing an ethanol solution of phenol-formaldehyde resin onto this surface, air drying for about eight minutes, and then curing the resin at 325 F. for twenty minutes. At the end of an identical chilling period it was found that the material adhering to the plastic coating was not a continuous wax film but comprised only normal wettage of the slurry and that this deposit weighed only 0.043 gram per three square inches of surface area.

EXAMPLE II In order to demonstrate the eflicacy of phenol-formaldehyde polymer to resist the solvent action of a ketone dewaxing solvent, a series of black iron strips were coated with phenol-formaldehyde polymer and other plastics, and the strips immersed in a mixture of waxy oil and dewaxing solvent in the proportion of 3.3 volumes of solvent per volume of oil. In these tests also the dewaxing solvent used contained 50 volume percent methyl-ethyl ketone, 29 volume percent benzol, and 21 volume percent toluol. Tests were conducted both at room temperature and at elevated temperatures. During the elevated temperature tests the mixture was heated to approximately its boiling point (about 180 F.) for eight hours during each day. These tests are set forth in Table I below.

Table I Immersion Test Plastic and Cure Six Weeks Ten Weeks at at Room Elevated Temperature Temperature Phenol-formaldehyde resin cured for No change No change.

20 minutes at 325 F. Epoxy resin (bisphenolepichlorhydrin do Suriaee (lulled condensate) cured for 15 minutes at and made porous. Epoxy resin (air dry formulation) softened in a without baking. few minutes. Melamine alkyd resin cured for 15 Softened 15 minutes at 300 F. Melamine alkyd resin cured for 20 No change softened after minutes at 325 F. two days. Butadiene copolymer cured 30 to 60 Roughened Do.

minutes at 325 F. Surface.

While there have been illustrated specific embodiments of the present invention, it will be understood that the invention is not to be limited to such specific examples. The invention is applicable to any solvent dewaxing process utilizing a dewaxing solvent in which a mixture of solvent and waxy oil is subjected to chilling. The degree of chilling or the particular composition of dewaxing solvent used is immaterial, as the phenol-formaldehyde polymer is effective in retarding wax deposition under any normal solvent dewaxing conditions.

What is claimed is:

1. In a solvent dewaxing process utilizing a dewaxing solvent wherein a mixture of wax, oil, and solvent is chilled, by indirect heat exchange, the improvement of carrying out said chilling while said mixture is in contact with a heat transfer surface coated with phenolformaldehyde polymer.

2. In a solvent dewaxing process utilizing a dewaxing solvent wherein a mixture of wax, oil, and solvent is chilled while in contact with a metal heat transfer surface and wherein only a portion of said metal surface is subject to scraping action, the improvement of carrying out said chilling while the portion of said surface not subject to scraping is coated with phenol-formaldehydepolymer.

3. In a solvent dewaxing process utilizing a solvent comprising a ketone wherein a mixture of wax, oil, and solvent is chilled by indirect heat exchange, the improvement of carrying out said chilling while said mixture is in contact with a heat transfer surface coated with phenolformaldehyde polymer.

4. In a solvent dewaxing process utilizing a solvent comprising a ketone wherein a mixture of wax, oil, and solvent is chilled by indirect heat exchange, the improvement comprising the steps of maintaining the mixture of wax and solvent being chilled at a pH of at least 6 and carrying out said chilling while said mixture is in contact with a metal heat transfer surface coated with phenol-formaldehyde polymer.

5. The process according to claim 4 wherein said ketone is methyl-ethyl ketone.

6. In a solvent dewaxing process untilizing a solvent comprising a ketone wherein a mixture of wax, oil, and solvent is chilled by indirect heat exchange in a chilling zone comprising linear paths through which said mixture flows, said linear paths being connected by arcuate paths, the improvement comprising maintaining a layer of phenol-formaldehyde polymer on the internal surface of said arcuate paths during said chilling process.

7. A chiller for precipitating wax from a mixture comprising wax and a ketone, said chiller comprising a plurality of pairs of substantially rectilinear opposed tubular pipes, through which said mixture is passed, and a U- shaped connecting tube between each member of said pairs, the internal surface of said connecting tubes being coated with phenol-formaldehyde polymer.

8. Apparatus according to claim 7, including means for scraping the internal surface of said substantially rectilinear pipes, said means being coated with phenolformaldehyde polymer.

9. The process of claim 6 wherein said layer has a thickness of from about'0.001 to about 0.002".

10. The apparatus according to claim 7 wherein said layer has a thickness of about 0.001 to about 0.002".

References Cited in the file of this patent UNITED STATES PATENTS 1,472,868 Hapgood Nov. 6, 1923 1,571,943 Hall et a1. Feb. 9, 1926 2,191,909 Ewer Feb. 27, 1940 2,224,109 Stearns Dec. 3, 1940 2,584,966 Reeves Feb. 5, 1952' 

1. IN A SOLVENT DEWAXING PROCESS UTILIZING DEWAXING SOLVENT WHEREIN A MIXTURE OF WAX, OIL, AND SOLVENT IS CHILLED, BY INDIRECT HEAT EXCHANGE, THE IMPROVEMENT OF CARRYING OUT SAID CHILLING WHILE SAID MIXTURE IS IN CONTACT WITH A HEAT TRANSFER COATED WITH PHENOLFROMALDEHYDE POLYMER. 